This invention relates to a method of recovering oil from subterranean formations with surfactant flooding systems that incorporate water soluble surfactants produced from an alkylphenol and kraft lignin.
Surface active compounds or surfactants have become extremely important chemicals in our society. Numberless types of surfactants are used for a myriad of applications. To work effectively, surfactants require water soluble and oil soluble characteristics. It is these mixed characteristics which enable surfactants to lower the interfacial tension between two disparate liquids.
One problem with many surfactants is their high cost of manufacture. Surfactants which are relatively cheap have an inherent advantage in the market place.
A minor use of surfactants has been in surfactant flooding systems for enhanced oil recovery. Because of the relatively high cost of surfactants, surfactant flooding systems for oil recovery have generally not been economical. The economics of surfactant flooding have additionally become more unfavorable recently with the low price of oil. But it is hoped that surfactant use in enhanced oil recovery will expand in the future.
Surfactant flooding to recover oil has been actively investigated due to the relatively poor ability of water floods to displace remaining oil from a reservoir's pore structure. Because of the structure of the reservoir and relative interfacial tensions involved, the flood water may form channels or fingers, bypassing the oil in the formation. Even where water has flowed, residual oil is trapped in pores by viscous and capillary forces. Further flooding with water will not remove such oil.
Investigations of ways to increase oil recovery by improving the displacement ability of water floods have produced useful surfactants which reduce the interfacial tension between oil and water in the reservoir. With lower interfacial tensions, oil that is trapped in the pore structure can be dispersed into the water as smaller and more easily deformable droplets. Many types of surfactants have been investigated and the choice of which surfactant to employ in a water flood operation is dependent upon reservoir characteristics as well as the cost and availability of the surfactants.
Most surfactant floods have employed a petroleum sulfonate as a sole surfactant, or at least a major component of a mixture of surfactants. Synthetic alkyl benzene sulfonates and alkyl sulfonates and sulfates have also been proposed as oil recovery surfactants. To combat separation problems in surfactant mixtures, especially at high salinities (&gt;2% salt), a material with both water soluble and oil soluble characteristic sulfonate surfactant mixtures. These materials are generally referred to as "solubilizers" and are usually sulfate or sulfonate salts of polyethoxylated alcohols or alkylphenols. The choice and concentration of solubilizer employed is dependent upon the choice of surfactants used, their overall concentration, and salinity.
U.S. Pat. No. 4,444,562 discloses a thermosol dyeing process for textiles which uses a reaction product formed by reacting an alkylphenol having from 1 to 4 carbons in the alkyl chain with formaldehyde and then with a lignosulfonate. The patent only discloses use in a fabric dyeing, which requires high water solubility. Consequently, highly polar lignosulfonates only are reacted with short chain alkylphenols to produce highly water soluble products.